The present invention relates to AC voltage regulators and more specifically to voltage regulators such as would be used on snowmobiles or motorcycles or other small vehicles where the headlamp and taillamp are normally operated directly from the coil of an alternator as opposed to the battery operated systems on most automobiles. Regulators for this purpose are described for example, in my prior U.S. Pat. Nos. 3,757,199; 3,755,685 and 3,755,709. While these systems have proved both workable and commercially practical, it is the purpose of the present invention to increase the accuracy and allow adaptation .Iadd.of similar techniques .Iaddend.in applications such as for instance, with low voltage lamps, say typically 6 volt systems where applications of the previous art .[.is more.]. .Iadd.has heretofore been .Iaddend.difficult. The amplifying circuits interposed between the RMS sensitive network and the shunt switching device .Iadd.employed in the circuits shown .Iaddend.in the references just mentioned generally are limited to relatively little output and therefore require shunt switching devices of high input sensitivity. These circuits typically use an SCR of 3 milliamperes or less maximum gate current to fire, and in some cases, under 1 milliampere.
Circuits of the present invention are usable with more readily available and higher current SCR's, the practical gate sensitivity range approaching 10 milliamperes. Also, the calibration of the previously mentioned art is somewhat dependent upon the characteristics of the alternator supplying the power for the system, therefore in some cases, requiring different calibration points for use with different alternators to produce the same regulated voltage. Therefore, the further object of this invention is to produce a regulator with minimum sensitivity to the characteristics of the alternator being regulated.
In U.S. Pat. No. 3,755,709 note that the gate drive current for the SCR must flow through either R-1 or L which comprise a portion of the voltage sensing network of the regulator. This current .Iadd.is .Iaddend.therefore reflected into the impedance of this sensing circuit node produces a voltage drop dependent upon the gate sensitivity of the SCR which varies from unit to unit and with temperature, thus producing unwanted deviation from ideal regulation. Also in that reference, the output of the bridge circuit is imposed directly across the base emitter junction of a transistor. This produces two undesirable effects. First, the well known temperature coefficient of the base emitter junction of a bipolar transistor produces a change in regulated voltage with temperature; secondly, since a finite voltage, say typically half of a volt, is required to bias on the base emitter junction, the bridge circuit does not operate at a true null, so the regulation point is dependent upon the RMS voltage applied as is desirable, but also somewhat upon the instantaneous peak applied to the bridge to produce sufficient output signal to drive this junction. It is therefore the object of this invention to overcome both of these limitations. Also in the previous reference, the power sensitive impedance L is equally responsive to the positive and negative portions of the input waveform because R-1 is a linear resistor. It is another and further object of .Iadd.the .Iaddend.present invention to make the response of the sensor slightly offset to favor one polarity of the waveform so as to reduce .[.an.]. .Iadd.any .Iaddend.instability that might otherwise result at the point where the alternator has only slightly more output than required by the lamps or other loads connected.
Another and further object of the present invention is to reduce the requirements, and therefore chance of failure on the amplifying devices typified by the transistor in U.S. Pat. No. 3,755,709. As previously mentioned, considerable output is needed from the bridge circuit in that case requiring a fairly large voltage across L and R3. Therefore.Iadd., .Iaddend.with a rapid increase in the output of the alternator, sensor L" may not respond fast enough to prevent .[.voltage.]. .Iadd.voltages .Iaddend. across the base emitter junction of the transistor, particularly in the reverse direction, from exceeding safe levels. For the same reasons, even during steady state .[.operation.]. .Iadd.operations .Iaddend.a major portion of the alternator supply voltage will appear from the base to the collector of that transistor. As will be seen in the description of the subsequent figures, the voltage requirements are greatly reduced .[.by the methods of.]. .Iadd.in accordance with .Iaddend.the present invention.
.Iadd.It is a further object of this invention to reduce the number and complexity of the circuit elements required in prior art circuit solutions to the problems of AC voltage regulation. For example, the present invention utilizes the power from the AC waveform for energizing the sensing circuitry, whereas other prior art circuitry requires rectification of the AC into DC power for the sensing circuitry, as for example the disclosure of Oltendorf in U.S. Pat. No. 3,538,427.
See also the disclosures of Elliot et al in U.S. Pat. No. 3,641,397; Hutchinson in U.S. Pat. No. 3,790,856; Digniffe in U.S. Pat. No. 3,742,237; Mills in U.S. Pat. No. 3,241,044 and Lorenz in U.S. Pat. No. 3,469,177 and Minks in U.S. Pat. No. 3,755,709.